HERMODYNAMIC CALCULATIONS OF THE INTERACTION OF SILICON AND BORON CARBIDES WITH IONIC MELTS
Abstract
To confirm the concept of the occurrence of intrinsic electrochemical potential and surface conductivity in silicon and boron carbides as a result of redox processes occurring at the semiconductor-ionic melt interface, a thermodynamic and corrosion study of the behavior of dispersed silicon and boron carbides materials in ionic melts was performed. A thermodynamic analysis of possible reactions of the interaction of silicon and boron carbides with oxygen-containing compounds of groups IV–VI elements was performed. Calculations showed that the most energetically beneficial process will be the oxidation of silicon carbide to metasilicate or silicon oxide, as well as the oxidation of boron carbide to metaborate or boron oxide. The reduction of the compound of the VI group element and Carbon will preferably take place before the release of this element in the free state or in the form of an oxide of the element in an intermediate state of oxidation. At temperatures of 900–1100 K, silicon and boron carbides should actively interact with all the considered compounds. The rate of corrosion of SiC of 400/315 dispersion value and of B4C of 315/250 dispersion value in melts of different composition was evaluated. The results of thermodynamic analysis and of the study of the chemical behavior of silicon and boron carbides in various melts show that, at the semiconductor-melt interface in contact with “soft” oxidants, redox processes take place, as well as electrochemical equilibrium and spatial separation of charges occur. In contact with “strong” oxidants, noticeable corrosion is observed. The results of the performed thermodynamic calculations make it possible to predict the possibility of controlling the potentials of silicon and boron carbides in ionic melts and of the implementation of processes of electrochemical metallization of these dielectrics with refractory metals and their carbides. In particular, the obtained results are used to substantiate the electrodeposition of galvanic coatings of molybdenum, tungsten and their carbides from ionic melts.
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